1. Field of Industrial Application
This invention relates to magnetic tape cassettes, and more specifically to a novel compact magnetic tape cassette or audio device or the like which is equal to or smaller than the "Phillips" type magnetic tape cassette in size.
2. Conventional Magnetic Tape Cassettes
Recently, cassette tape recorders have been remarkably decreased both in size and in weight, and magnetic tape cassettes therefore have also been miniaturized, In addition, in the field of audio technique, there has been a strong demand for the provision of magnetic tape cassettes which are suitable for high-quality, high-density recording and reproducing operations of long period. In order to satisfy this requirement, a magnetic tape cassette has been proposed in the art which is operated according to a digital system such as a pulse code modulation (PCM) system in which, unlike an analog system, input signals are converted into pulse signals to perform signal recording and reproducing operations. In the magnetic tape cassette, the recording frequency band of the magnetic tape therein must be about five times as wide as that of a conventional audio tape. For this reason, large video tape cassettes wider in recording frequency band than the audio compact cassettes have been extensively employed.
Video tape cassettes, except for special ones, are operated using the rotary head system, The video tape cassettes are provided with a guard panel which is adapted to close the opening formed in the front part of the cassette and is swingable towards the top of the cassette. That is, in the case of the magnetic tape cassette operated according to the digital system, high-density wide-frequency-band recording and reproducing operations, which are short in recording wavelength when compared with the conventional audio compact cassette, are carried out. Therefore, the cassette's structure should be such that the magnetic tape therein is sufficiently protected.
The magnetic tape cassette to which the technical concept of the invention is applied is one which, similar to the previously mentioned video tape cassette, is applicable to audio devices employing a relatively wide frequency band signal recording and reproducing system. In addition, the magnetic tape cassette is equal to or smaller than the conventional audio compact magnetic tape cassette in size; that is, the magnetic tape cassette is an extremely small one. Accordingly, it can be expected that similar to the conventional audio compact magnetic tape cassette, the extremely small magnetic tape cassette is frequently carried and used outdoors. Therefore, the cassette should have a structure which can positively prevent jamming of the magnetic tape which may be caused when the cassette is vibrated and slackened while being carried about.
One example of a magnetic tape cassette which has been proposed to meet the above-described requirement has a locking member. The locking member functions to lock the hubs, on which the magnetic tape has been wound, when the magnetic tape cassette is not being used, and to release the hubs when the casssette is used. The locking member is urged towards the hubs by a spring, so that, when the cassette is not being used, two protrusions of the locking member are abutted against the hubs, respectively, to stop the rotation of the hubs. When the cassette is used, the protrusions are moved away from the hubs. However, as the size of the cassette is decreased, its components are also miniaturized. Therefore, it is rather difficult to combine the locking member with the cassette body. Furthermore, as the locking member is combined with the cassette body while being urged by the spring. it is liable to come off during assembly, Thus, the locking member is one of the factors which make it difficult to assemble the magnetic tape cassette.
The conventional locking member has disadvantages during operation as well as during assembly of the cassette. During operation, the locking member is urged towards the hubs by a spring so that the locking member slides horizontally. However, the locking member is not supported in a vertical direction. Therefore, when the hubs are released, the locking member is bent causing the locking member's protrusion or flat part to contact the magnetic tape which is wound on the hubs. The contact can scratch tge magnetic tape. The contact can also apply an unwanted load to the magnetic tape. If the load is applied to the magnetic tape in this manner, then the magnetic tape cannot run at a constant speed, and it is impossible to perform signal recording and reproducing operations with high accuracy.